Human skin is a complex integration of different types of cells and tissues which form an organ. Skin is also the primary seat of the sense of touch and creates a covering for the protection of the deeper tissues. The skin also plays an important role in the regulation of body temperature and is also an excretory and absorbing organ. Skin consists primarily of a layer of vascular tissue and an external covering of epithelium known as the epidermis. On the surface layer are the sensitive papillae and alongside or imbedded beneath it are certain specialized organs, specifically the sweat glands, hair follicles, and sebaceous glands.
In order to defend the tissues below from trauma, the skin must be tough, flexible, and highly elastic. As a result of this function, injuries to the skin can occur. Wounds, which are caused by physical means, result in a disruption of the normal continuity of the structures of the skin. Examples of wounds include cuts, punctures, lacerations, etc.
Whereas skin is composed of an external covering of epithelium, the stomach lining is also composed of internal epithelium (endothelium). Gastric ulcers are a result of damage or erosion of the stomach lining. Gastric ulcers occur along the lesser curvature of the stomach where the pyloric glands border the oxyntic gland. They are usually 1 to 2.5 cm in diameter; however, they can vary from a few mm to several cm. Ulcers are usually round, oval or elliptical, with sharply defined margins. The surrounding mucosa is often hyperemic and edematous. Ulcers penetrate into the submucosa or muscular layer. A thin layer of gray or white exudate usually covers the base of the ulcers; this layer is composed of fibrinoid, granulation and fibrous tissue layers. During healing, fibrous tissue in the base contracts the ulcer and may distort the surrounding tissue. Healing continues as granulation tissue fills the base and epithelium from the ulcer edges cover its surface.
Healing usually requires two to six weeks but may require a longer time, especially if the ulcer is large or of a longstanding nature. If complete healing of the ulcer does not occur (as monitored by X-ray or endoscopic exam), surgery is usually considered in an effort to prevent complications or a prolonged, distressing course. The Merck Manual of Diagnosis and Therapy, 14th ed., by Merck Sharp & Dohme Research Laboratories (1982).
The mechanism of epithelial wound healing is a complex process involving ultrastructural changes of epithelial cells. These changes allow for detachment from neighboring cells, migration and subsequent reattachment. The migration of epithelial cells has been found to depend on a suitable matrix composed of fibrin, fibronectin or basement membrane which traverse the wound. Clark, R., J. Am. Acid Derm., 13:701-718 (1985); Zitelli, J., Adv. Dermatol. 2:243-268 (1987).
There are two types of healing processes: (1) primary union or first intention healing and (2) secondary union or second intention healing. Primary union occurs when a clean wound with a minimal loss of tissue heals together cleanly. The process involves clotting and formation of a crust or scab to seal the wound; an acute inflammatory reaction; reepithelialization of the surface and fibrous bridging due to fibrin followed by complete sealing of the wound by an epithelial covering. Thereafter, hair follicles, sebaceous glands and sweat glands may subsequently regenerate. The process of second intention healing requires the removal of necrotic debris. The gap in the wound then fills in with fibrous materials.
When dealing with gastric ulcers the major objectives of therapy are relief of pain and healing of the ulcer. In a number of countries (not the U.S.) carbenoxolene is used to treat gastric ulcers. Carbenoxolene is a hydrolytic product of glycyrrhizic acid (derivative of licorice); it has been shown to increase the rate of gastric ulcer healing. Braunwald, E., Harrison's Principles of Internal Medicine 11th ed. p. 1247. It appears to increase the life span of gastric mucosal epithelial cells and increase the secretion and viscosity of gastric mucus. However, carbenoxolene has aldosterone-like effects, therefore it tends to increase the rate at which the body retains sodium and water. These effects may be blocked by aldosterone-antagonists, however the antagonists obliterate the healing effects of the carbenoxolene. There is a need for therapies which can promote healing without the negative side effects.
It has recently become clear that the skin may be a target tissue for 1,25--(OH).sub.2 -D.sub.3 (Stumpf, W. E. et al., Science, 206:1188-1190 (1979)). Cells isolated from the skin of rats, mice, and humans, and from cultured human skin fibroblasts and keratinocytes contain a high affinity (1.0.times.10.sup.-10 M) low capacity receptor-like protein for 1,25-dihydroxyvitamin D.sub.3 (Franceschi, et al., Arch. Biochem. Bioshys., 210: 1-13 (1979); Simpson, R. U. et al., P.N.A.S. (USA), 77: 5822 (1980); Colston, K. et al., Endocrinology, 107: 1916 (1980); Feldman, D. et al., Journal of Clinical Endocrinology & Metabolism, 51: 1463 (1980); Eil, C. et al., P.N.A.S. (USA), 78: 2562 (1981); and Clemens, T. L. et al., J. Clin. Endocr. Metab. 56: April 1983)). A specific biological function for 1,25--(OH).sub.2 -vitamin D.sub.3 in the skin, however, has yet to be discovered. Nevertheless, evidence has come forth supporting the concept that the dihydroxy metabolite of the vitamin does have biologic actions in the skin. This evidence was obtained evaluating the biological activity of 1,25-dihydroxy vitamin D.sub.3 simultaneously in cultured human skin fibroblasts that either possessed or lacked a cytosolic receptor-like protein for the hormone (Clemens, T. L. et al., J. Clin Endocrinol. Metab., 56: April 1983). The receptor-negative skin fibroblasts were obtained from a patient with a rare bone disorder called vitamin D dependent rickets, type II, a heritable disorder caused by a defective or complete absence of a cytoplasmic or nuclear receptor for 1,25-dihydroxyvitamin D. Administration of the dihydroxy metabolite of vitamin D.sub.3 caused a dose-dependent inhibition of cell growth in receptor positive skin fibroblasts (about 40-50% reduction in cell growth was observed in cultures containing 10.sup.-6 and 10.sup.-8 M of hormone and 12% in cultures containing 10.sup.-10 M of 1,25--(OH).sub.2 -D.sub.3), and, by contrast, had absolutely no effect on the growth of receptor negative skin fibroblasts.
Holick et al. (New England Journal of Medicine, 303:349-354 (1980)) have studied the feasibility of using the skin as an organ for the synthesis and absorption of vitamin D metabolites. These investigators demonstrated that topical application of various vitamin D metabolites or pro-vitamin forms followed by phototherapy results in elevated serum levels of dihydroxyvitamin D.sub.3. It was therefore suggested that topical application of vitamin D analogues may be an effective method of therapy for diseases involving calcium, phosphorous and bone metabolism problems.
Holick, U.S. Pat. No. 4,410,515, discloses vitamin D glycosides and their use in the regulation of calcium metabolism and phosphorous homeostasis.
Holick, U.S. Pat. No. 4, 521,410, discloses water-soluble glycosyl orthoesters of vitamin D and their use in the regulation of calcium metabolism and phosphorous homeostasis.
Holick, U.S. Pat. No. 4,335,120, discloses that the toxic effects of orally administered vitamin D.sub.2 and vitamin D.sub.3 compounds can be avoided by topical administration whereby a slow and controlled transportation of the vitamin D compounds into the blood stream of a subject is achieved.
Jackson, U.S. Pat. No. 3,655,881 (1972) discloses methods for treating burned skin by inducing a state of calciphylaxis. Calciphylaxis is a hypersensitivity reaction resulting from the administration of or endogenous production of a sensitizing calcifier in combination with a challenger. Sensitizing calcifiers include, inter alia, vitamins D.sub.2 and D.sub.3.
Dikstein, U.S. Pat. No. 4,610,478, and European Patent Application No. 0 129 003 (1984), discloses compositions containing 1-alpha-hydroxycholecalciferol or 1-alpha,25-dihydroxycholecalciferol for the topical treatment of skin disorders, such as dermatitis, psoriasis, eczema, solar keratosis and certain stages of wound healing and alopecia. Dikstein also teaches that low dosages are required, from about 0.03 .mu.g to 1.0 .mu.g per gram of composition, to minimize the risk of undesired side effects and systemic effects. However, Dikstein does not teach that vitamin D compounds are useful for the treatment of wounds caused by lacerations, punctures or cuts.
Additionally, no specific therapy is available for healing decubitus or diabetic ulcers of the feet, however it is suggested that a course of aggressive supportive treatment can lead to salvaging the limb. Therefore, a need exists for effective treatments for diabetic ulcers.